1. Field of the Invention
The present invention relates to a method for driving a flat-type display device.
2. Description of Related Art
As image display devices which will possibly replace cathode-ray tubes (CRTs) currently widely spread, flat (flat panel type) display devices are vigorously studied. Examples of the flat display devices include a liquid crystal display (LCD), an electroluminescence display (ELD), and a plasma display (PDP). In addition, flat display devices having incorporated therein a cathode panel having an electron emission device are also developed. As electron emission devices, a cold cathode field emission device, a metal/insulating film/metal element (also called an MIM element), and a surface conductive-type electron emission device are known, and a flat display device having incorporated therein a cathode panel having the above electron emission device composed of a cold cathode electron source has attracted attention since it advantageously achieves color display with high resolution and high luminance and causes low power consumption.
A cold cathode field emission display device (hereinafter, frequently referred to simply as “display device”) is a flat display device having incorporated therein a cold cathode field emission device as an electron emission device. This type of display device generally has a structure having a cathode panel CP and an anode panel AP disposed so that they face each other through a high-vacuum space, and joined together at their edges through a joint member. The cathode panel CP has a plurality of cold cathode field emitter elements (hereinafter, frequently referred to simply as “field emitter element(s)”), and the anode panel AP has a fluorescent region with which electrons emitted from the field emitter elements collide and which is excited to emit light. The cathode panel CP has electron emitter areas being arrayed in a two-dimensional matrix form and corresponding to respective subpixels, in which each electron emitter area has formed one or a plurality of field emission devices. Examples of field emitter elements include those of Spindt type, flattened type, edge type, or flat type.
A schematic fragmentary end view of a typical display device having a Spindt-type field emission device as an example is shown in FIG. 10, and a partial, schematic exploded perspective view of a cathode panel CP and an anode panel AP separated from each other is shown in FIG. 19. The Spindt-type field emission device constituting the display device includes a cathode electrode 11, an insulating layer 12, a gate electrode 13, openings 14, and a conical electron emitter 15. Herein, the cathode electrode 11 is formed on a support 10. The insulating layer 12 is formed on the support 10 and the cathode electrode 11. The gate electrode 13 is formed on the insulating layer 12. The openings 14 are formed in the gate electrode 13 and insulating layer 12, in which a first opening 14A formed in the gate electrode 13 and a second opening 14B formed in the insulating layer 12. The conical electron emitter 15 is formed on the cathode electrode 11 at the bottom of each opening 14.
A schematic fragmentary end view of a display device having a so-called flattened field emission device having a substantially planar electron emitter 15A is shown in FIG. 18. This field emission device is similar to the Spindt-type field emission device as described above, and is different in having an electron emitter 15A formed on the cathode electrode 11 at the bottom of each opening 14, instead of the electron emitter 15. The electron emitter 15A is composed of, for example, a number of carbon nanotubes, part of which is buried in the matrix.
An interlayer dielectric layer 16 is formed on the insulating layer 12 and the gate electrode 13, and an opening (third opening 14C) communicating with the first opening 14A formed in the gate electrode 13 is formed in the interlayer dielectric layer 16, and further a focusing electrode 17 is formed over the interlayer dielectric layer 16 and the sidewall of the third opening 14C. In FIGS. 18 and 19, the interlayer dielectric layer and the focusing electrode are not shown.
In these display devices, the cathode electrode 11 is in the form of a strip extending in the Y direction, and the gate electrode 13 is in the form of a strip extending in the X direct ion different from the Y direction. Generally, the cathode electrode 11 and the gate electrode 13 are formed in strips in respective directions such that the images from the electrodes 11, 13 cross at a right angle. The overlap region where the strip-form cathode electrode 11 and the strip-form gate electrode 13 overlap is an electron emitter area EA, and corresponds to one subpixel. The electron emitter areas EA's are generally arrayed in a two-dimensional matrix form in an effective region EF of the cathode panel CP. The effective region EF means a display region at the center having a practical function of the flat-type display device, i.e., display function. A non-effective region NE is present on the outside of the effective region EF and in the form of a frame surrounding the effective region EF.
On the other hand, the anode panel AP has a structure including fluorescent regions 22 having a predetermined pattern formed on a substrate 20 in which the fluorescent regions 22 are covered with an anode electrode 24. The fluorescent regions 22 specifically include a red light-emitting fluorescent region 22R, a green light-emitting fluorescent region 22G, and a blue light-emitting fluorescent region 22B. A light absorbing layer (black matrix) 23 composed of a light absorbing material, such as carbon, is buried between the fluorescent regions 22 to prevent the occurrence of color mixing in the display image, i.e., optical cross talk. The fluorescent regions 22 constituting one subpixel are individually surrounded by a barrier 21, and the barrier 21 has a flat form of lattice-like form, that is, form of parallel crosses. In the figure, reference numeral 40 designates a spacer, and reference numeral 26 designates a joint member. In FIGS. 18 and 19, the barrier and spacer are not shown.
One subpixel is composed of the electron emitter area EA on the cathode panel side, and the fluorescent region 22 on the anode panel side opposite (facing) the above electron emitter area EA. The pixels on the order of, e.g., several hundred thousand to several million are arrayed in the effective region EF. In the display device making color display, one pixel is composed of an assembly of a red light-emitting subpixel, a green light-emitting subpixel, and a blue light-emitting subpixel. The anode panel AP and the cathode panel CP are arranged so that the electron emitter area EA and the fluorescent region 22 face each other, and they are joined together at their edges through the joint member 26, followed by evaluation and sealing, thus producing a display device. A space between the anode panel AP, the cathode panel CP, and the joint member 26 is a high vacuum (e.g., 1×10−3 Pa or less).
Therefore, the spacer 40 must be placed between the anode panel AP and the cathode panel CP for preventing the display device from suffering damage due to atmospheric pressure. Generally, an antistatic film (not shown in the figures) comprised of, e.g., CrOx or CrAlxOy is formed on the sidewall of the spacer 40.
In driving the display device, a linear sequential driving mode is frequently employed. The linear sequential driving mode is a mode in which, among a group of electrodes crossing in a matrix form, for example, the gate electrodes 13 are used as scanning electrodes (the number of M) and the cathode electrodes 11 are used as data electrodes (the number of N), and the gate electrodes 13 are selected and scanned and an image is displayed according to a signal to the cathode electrodes 11 to constitute one frame. In the linear sequential driving mode, electron emission from each electron emitter area EA is performed in a selected time of the scanning electrode, i.e., only in a so-called duty period of the scanning electrode. The duty period is a value in terms of second obtained by dividing a refresh time (e.g., 16.7 msec at 60 Hz) of a frame by M.
More specifically, a relatively negative voltage is applied to the cathode electrode 11 from a cathode electrode control circuit 31, and a relatively positive voltage is applied to the gate electrode 13 from a gate electrode control circuit 32. For example, 0 V is applied to the focusing electrode 17 from a focusing electrode control circuit 33, and a positive voltage higher than the voltage applied to the gate electrode 13 is applied to the anode electrode 24 from an anode electrode control circuit 34. In display made by the display device, a video signal is input into the cathode electrode 11 from the cathode electrode control circuit 31, and a scanning signal is input into the gate electrode 13 from the gate electrode control circuit 32. An electric field resulting from applying a voltage across the cathode electrode 11 and the gate electrode 13 causes the electron emitter 15 or 15A to emit electrons due to a quantum tunnel effect. The electrons are attracted by the anode electrode 24 and pass through the anode electrode 24 and collide with the fluorescent regions 22, so that the fluorescent regions 22 are excited to emit light, thus obtaining a desired image. Accordingly, the operation of the cold cathode field emission display device is basically controlled by changing the voltage applied to the gate electrode 13 and the voltage applied to the cathode electrode 11.
When electrons emitted from the electron emitter areas EA near the spacer 40 pass through the anode electrode 24 in the anode panel AP and collide with the fluorescent regions 22, part of the electrons backscatter at the fluorescent regions 22 and part of the resultant backscattering electrons collide with the spacer 40. Consequently, gas adsorbed on the spacer 40 is released, and molecules of the gas and others are attached to or adsorbed on the surface of the electron emitter 15 or 15A constituting the electron emitter areas EA near the spacer 40, causing a phenomenon such that the electron emission properties of the electron emitter 15 or 15A deteriorate. Such a phenomenon lowers electron emission from the electron emitter areas EA near the spacer 40, so that a difference is caused between the light emission conditions in the fluorescent regions 22 near the spacer 40 and the light emission conditions in the fluorescent regions 22 which are not near the spacer 40 or are far away from the spacer 40.
This state is diagrammatically shown in FIG. 20A. In FIG. 20A, a relative anode current flowing between the electron emitter area and the anode electrode due to the electrons emitted from each electron emitter area is taken as the ordinate (relative anode current). The numbers assigned to the positions of the electron emitter areas near the spacer in the Y direction are taken as the abscissa, and an electron emitter area having the smaller number is nearer the spacer. From FIG. 20A, it is found that the amount of electrons emitted from the electron emitter areas near the spacer is smaller than the amount of electrons emitted from the electron emitter areas far away from the spacer.
The conditions of electron emission from the electron emitter areas change with time. This state is diagrammatically shown in FIG. 20B. In FIG. 20B, a value obtained by dividing a value of anode current flowing between the electron emitter area and the anode electrode due to the electrons emitted from the electron emitter areas near the spacer by a value of anode current flowing between the electron emitter area and the anode electrode due to the electrons emitted from the electron emitter areas far away from the spacer is taken as the ordinate (relative anode current ratio), and a lapse of time (unit: optional) is taken as the abscissa. From FIG. 20B, it is found that, as a period of time lapses, the decrease of the anode current flowing between the electron emitter area and the anode electrode due to the electrons emitted from the electron emitter areas near the spacer becomes larger than the decrease of the anode current flowing between the electron emitter area and the anode electrode due to the electrons emitted from the electron emitter areas far away from the spacer. In other words, it is found that, as a period of time lapses, a difference is caused between the change of the electron emission properties in the electron emitter areas near the spacer and the change of the electron emission properties in the electron emitter areas far away from the spacer.
A method for solving the above problem is disclosed in, for example, Japanese Translation of PCT International Application (KOHYO) No. 2004-534968.